Lack of time is the number one reason people give for not exercising. And lack of results once they do start exercising isn’t far behind. Interval training is a great solution for both of these common problems.

Interval training involves alternating short bursts of intense activity with what is called active recovery, which is typically a less-intense form of the original activity.

The Swedes came up with a term for this type of training: Fartlek, which means speed play. Not only is it an efficient training method, Fartlek training can help you avoid injuries that often accompany non-stop, repetitive activity, and provides the opportunity to increase your intensity without burning yourself out in a matter of minutes.

Unlike traditional interval training, Fartlek training does not involve specifically or accurately measured intervals. Instead, intervals are based on the needs and perceptions of the participant. In other words, how you feel determines the length and speed of each interval.

Advantages of Intervals

Interval training utilizes the body’s two energy-producing systems: the aerobic and the anaerobic. The aerobic system is the one that allows you to walk or run for several miles and uses oxygen to convert carbohydrates from various sources throughout the body into energy.

The anaerobic system, on the other hand, draws energy from carbohydrates stored in the muscles (in the form of glycogen) for short bursts of activity such as sprinting, jumping or lifting heavy objects. This system does not require oxygen, nor does it provide enough energy for more than the briefest of activities. And its by-product, lactic acid, is responsible for that achy, burning sensation in your muscles that you feel after running up several flights of stairs, for example.

Interval Basics

Interval training allows you to enjoy the benefits of anaerobic activities without having to endure those burning muscles. In its most basic form, interval or Fartlek training might involve walking for two minutes, running for two, and alternating this pattern throughout the duration of a workout.

The intensity (or lack thereof) of each interval is up to how you feel and what you are trying to achieve. The same is true for the length of each interval. For example, if it is your habit to walk two miles per day in 30 minutes, you can easily increase the intensity of your walk (as well as up its calorie-burning potential) by picking up the pace every few minutes and then returning to your usual speed.

A great trick is to tell yourself that you’ll run a particular distance, from the blue car to the green house on the corner, for example, and then walk from the green house to the next telephone pole.

When you first start Fartlek training, each interval can be a negotiation with yourself depending on how strong or energetic you happen to feel during that particular workout. This helps to break up the boredom and drudgery that often comes from doing the same thing day after day.

A More Advanced Approach

Despite its simplicity, it also is possible to take a very scientific approach to interval training, timing both the work and recovery intervals according to specific goals. Keep the four variables listed in the box to the left in mind when designing an interval-training program.